This invention relates to the making of foams from unsaturated polyester resins. More particularly, it relates to compositions useful in methods for creating a foam structure in polyester resin products by providing a source of gas for expansion of the resin.
There is a well developed body of prior art designed to foam unsaturated polyester resins with gaseous blowing agents. Over the years unsaturated polyesters have been foamed by generating CO.sub.2 gas through the acid decomposition of carbonate and bicarbonate salts. Typically the carbonate salt per se is mixed directly into the unsaturated resin mass and acid added. Typical references employing such techniques include U.S. Pat. Nos. 3,479,303, 4,016,112, 4,028,289, 4,119,583, 4,122,047, 4,347,331 and British Pat. No. 2,029,834.
To date there has been only limited commercial success utilizing carbonate salts for generating CO.sub.2. One of the drawbacks which apparently limits wide spread industry acceptance of the process includes the requirement for a significant amount of acid such as acetic acid and water to be added to the resin to help solubilize the carbonate granules and to start their decomposition for gas formation. In general, there has been a lack of consistent results in terms of the desired uniform foam structures. This lack of uniformity is most likely due to difficulties in dispersing a relatively coarse inorganic salt in the organic medium presented by the unsaturated polyester resin.